Naturally Occurring Elettaria cardamomum Extract as

International Scholarly Research Network
ISRN Corrosion
Volume 2012, Article ID 971650, 6 pages
doi:10.5402/2012/971650
Research Article
Naturally Occurring Elettaria cardamomum Extract as
a Corrosion Inhibitor for the Dissolution of Zinc in 1.0 M HCl
M. Sobhi
Department of Chemistry, Faculty of Science, Benha University, Benha 13518, Egypt
Correspondence should be addressed to Mohamed Sobhi, [email protected]
Received 21 September 2012; Accepted 8 October 2012
Academic Editors: N. Boshkov, I. Obot, and Q. Qu
Copyright © 2012 M. Sobhi. This is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The inhibitive action of water extract of naturally occurring Elettaria cardamomum plant against the corrosion of zinc in 1.0 M
HCl solution was investigated using weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy.
From these measurements, it was found that the values of surface coverage (θ) and inhibition efficiency increase with increasing
the concentration of the extracted compound. The activation energy of the corrosion was calculated and it was found that the
presence of the extracted compound in 1.0 M HCl solutions increases the values of activation energy. The inhibiting effect of this
extract results from its adsorption on the electrode surface via the adsorption centers of the compounds present in the extract.
The adsorption of this extract compound onto the surface of zinc follows the Langmuir adsorption isotherm. The thermodynamic
parameters were calculated for the tested system from the data obtained at different temperatures.
1. Introduction
Corrosion of zinc has been a subject of numerous studies
due to its high technological value and wide range of industrial applications and economic importance; its protection
against corrosion has attracted much attention. The use of
inhibitors is one of the most practical methods for protection
against corrosion especially in acidic media [1]. Most of
the well-known corrosion inhibitors are organic compounds
containing nitrogen, sulphur, and oxygen atoms [2–7]. This
study sets out to develop a safe method of corrosion protection, harmless to nature but still effective against corrosion,
by searching for natural products. The purpose of this study
wants to discover new, environmentally friendly corrosion
inhibitors, that is, material protection compounds, based
on components from naturally occurring. Recently, plant
extracts have again become important as an environmentally
acceptable, readily available, and renewable source for a wide
range of needed inhibitors. Plant extracts are viewed as
an incredibly rich source of naturally synthesized chemical
compounds that can be extracted by simple procedures with
low cost [8].
Elettaria cardamomum Maton is an important member
of the family Zingiberaceae. The seeds contain essential oil
in concentration of about 4% of dry weight. The main
compound is 1,8-cineole (representing 50% or more), with
smaller amounts of α-terpineol and limonene [9, 10].
The present work aims to study the effect of dry fruits
extracts of E. cardamomum as a corrosion inhibitor for
the corrosion of zinc in 1.0 M HCl. Moreover, the effect
of temperature on the dissolution of zinc as well as on
the inhibition efficiency of the used compound was also
investigated.
2. Experimental
2.1. Medium. The aggressive solution of 1.0 M HCl was
prepared by dilution of analytical grade HCl (37%) with
double distilled water and all experiments were carried out
in unstirred solutions.
2.1.1. Extract Preparation. Dry fruits of E. cardamomum were
extensively washed under running tap water for removal
of dust particles and epiphytic hosts normally found on
the surface, followed by washing with sterilized distilled
water. They were further air-dried on filter paper at room
temperature and then powdered with the help of sterilized
2
ISRN Corrosion
The inhibition efficiency IE (%) was calculated from
polarization measurements according to the relation given
below:
CH3
HO
IE (%) =
O
CH3
Limonene
(2)
where Icorr and Icorr(inh) are uninhibited and inhibited corrosion current densities, respectively. They are determined
by extrapolation of Tafel lines to the respective corrosion
potentials.
CH3
1,8-cineole
Icorr − Icorr(inh)
× 100,
Icorr
α-terpineol
Scheme 1
pestle and mortar. Dry powder was further extracted by using
aqueous solvents [11, 12] as follows.
2.1.2. Aqueous Extraction. Air-dried powder (10 g) of the
respective plant part was mixed well in 100 mL sterilized
distilled water and kept at room temperature for 24 h on an
orbital shaker with 150 rpm. The solution was further filtered
using muslin cloth. The filtrate was centrifuged at 5000 rpm
for 15 min. The supernatant thus obtained was filtered
through Whatman’s filter no. 1, then the filtrate was collected
in a preweighed sterilized test tube. Aqueous extracts were
prepared in a final concentration of 100 mg/mL. The extract
main components have the formulas shown in Scheme 1.
2.2. Weight Loss Measurements. Zinc strips (99.99% pure),
with 3.0 × 2.0 × 0.05 cm sizes for each, were used for weight
loss measurements. Weight loss experiments were carried out
as described elsewhere [13]. The corrosion rate (CR) and
the percentage protection efficiency IE (%) were calculated
according to the following equations [14, 15]:
CR =
IE (%) =
Δm
,
St
CRcorr − CRcorr (inh)
× 100,
CRcorr
(1)
where Δm (mg) is the mass loss, S (dm2 ) is the area, t (h)
is the immersion period, and CRcorr and CRcorr(inh) are the
corrosion rates of zinc in the absence and presence of the
inhibitors.
2.3. Potentiodynamic Polarization. Potentiodynamic measurements were carried out using three-compartment glass
cell and PS remote potentiostat and PS6 software for calculation of electrochemical parameters. Platinum electrode was
used as a counter electrode (separated from the cell solution
by a sintered glass frit) and a saturated calomel electrode SCE
(inside a Luggin probe) as a reference electrode. A cylindrical
rod embedded in araldite with an exposed surface area of
0.5 cm2 was used. The electrode surface was polished with
different grades of emery paper, degreased with acetone, and
rinsed with distilled water.
2.4. Electrochemical Impedance Spectroscopy. The impedance
measurements were carried out at open circuit potential
(Eocp ) in the frequency range from 10 kHz to 100 mHz with
signal amplitude perturbation of 5 mV by using a computercontrolled potentiostat (Auto Lab 30, Metrohm). All experiments were performed using three-electrode system.
The surface coverage and the inhibition efficiency of the
inhibitor were calculated from the charge transfer resistance
values using the following equations:
θ=
(1/Rct )o − (1/Rct )
,
(1/Rct )o
(1/Rct )o − (1/Rct )
× 100,
IE (%) =
(1/Rct )o
(3)
where (Rct )o and (Rct ) are the uninhibited and inhibited
charge transfer resistance, respectively [16].
3. Result and Discussion
3.1. Weight Loss Measurements. The effect of addition of the
extracted compound on the weight loss of zinc strips in
1.0 M HCl as a corrosive medium was studied. The values
of percentage inhibition efficiency IE (%) and corrosion
rate (CR) obtained from weight loss method at different
concentrations of inhibitor at 30◦ C are summarized in
Table 1. It has been found that this compound inhibits
the corrosion of zinc in hydrochloric acid solution, at all
concentrations used in this study, that is, 100–500 ppm.
The data given in Table 1 reveals that the corrosion rate is
decreased from 252.9 to 16.20 mg dm−2 h−1 .
The mechanism of corrosion inhibition may be explained
on the basis of adsorption behavior [17]. The values of
surface coverage (θ = IE/100) for different concentrations
of the studied natural extract obtained from the weight loss
measurements at temperature range 303 K. Data were tested
graphically by fitting to various isotherms. A straight line
(Figure 1) was obtained on plotting Cinh versus Cinh /θ. From
this plot, it is observed that it obeys Langmuir’s adsorption
isotherm
θ=
Wo − W
.
Wo
(4)
3.2. Polarization Studies. The effect of addition of various
concentrations of the natural extracted compound on the
cathodic and anodic polarization curves of zinc in 1.0 M HCl
ISRN Corrosion
3
Table 1: Corrosion parameters for zinc in an aqueous solution of 1.0 M HCl in absence and presence of different concentrations of inhibitor
from weight loss measurements at 30◦ C for 1/2 h.
Weight loss (mg dm−2 )
843
311
206
151
74
54
Cinh (ppm)/θ
100
200
300
400
500
550
500
500
450
450
400
400
350
350
300
300
250
250
200
200
150
150
200
300
400
Cinh (ppm)
IE (%)
—
63.10
75.60
82.00
91.30
93.60
1.6
550
100
CR (mg dm−2 h−1 )
252.90
93.30
61.80
45.30
22.20
16.20
500
Figure 1: Langmuir’s adsorption isotherm plot for the adsorption
of inhibitor in 1.0 M HCl, on the surface of zinc.
solution at 30◦ C (Figure 2) was studied. Electrochemical
parameters such as corrosion current density (icorr ), corrosion potential (Ecorr ), Tafel constants (ba and bc ), and
percentage inhibition efficiency IE (%) were calculated from
Tafel plots shown in Table 2. It is evident from the table that
there is an increase in both anodic and cathodic Tafel slopes
upon addition of the inhibitor indicated a mixed anodic and
cathodic effect on the corrosion inhibition mechanism [18].
It is also observed from the table that the corrosion potential
shifted to more positive values and icorr decreased when the
concentration of the inhibitor was increased indicating the
inhibiting effect of this compound resulting in an increase on
IE (%) with the increase in the concentration of the additive.
3.3. Effect of Temperature. The effect of temperature is an
important parameter in studies on metal dissolution. The
corrosion rate in acid solutions, for example, increases exponentially with a temperature increase because the hydrogen
evolution overpotential decreases [19].
The effect of temperature on the corrosion parameters
such as icorr , Ecorr , and IE (%) was studied in 1.0 M HCl
alone and in the presence of 500 ppm of inhibitor over the
temperature ranges from 303 to 353 K.
The data listed in Table 3 show that Ecorr shifted to
more negative values, whereas the values of icorr increased
with the increase in temperature, but by different amounts,
indicating that the natural extracted compound affected the
1.2
log i (mA·cm−2 )
Inhibitor concentration (ppm)
Blank
100
200
300
400
500
1
2
3
0.8
4
5
6
0.4
0
−0.4
−0.8
−2000
−1600
−1200
−800
−400
0
E (mV SCE)
Figure 2: Potentiodynamic polarization curves of zinc electrode in
1.0 M HCl solution containing different concentrations of inhibitor
at 30◦ C. (1) 0.00 ppm, (2) 100 ppm, (3) 200 ppm, (4) 300 ppm, (5)
400 ppm, and (6) 500 ppm.
zinc electrochemical dissolution. On the other hand, the
increase in temperature led to a decrease in the inhibition
efficiency and the best inhibition efficiency was obtained at
303 K.
Arrhenius-type dependence is observed between the
corrosion rate and temperature which given by [20]
K=
Ae−Ea
,
RT
(5)
where K is the rate constant of the metal dissolution reaction
that is directly related to corrosion current density icorr [21],
A is the frequency factor, T is the absolute temperature,
and Ea is the activation energy. By plotting log K versus
1/T the values of Ea can be calculated from the slope of
the obtained straight lines (Figure 3). The Ea determined
from the Arrhenius plots corresponds to 9.832 kJ mol−1 in
the absence and 14.768 kJ mol−1 in the presence of inhibitor.
From the obtained values, it is clear that the presence of the
natural extracted compound increased the activation energy
values and consequently decreased the corrosion rate of
the metal. These findings indicate that extracted compound
acted as an inhibitor through increasing the activation energy
of metal dissolution by making a barrier to mass and charge
transfer by their adsorption on metal surface.
4
ISRN Corrosion
Table 2: Electrochemical parameters for zinc in absence and presence of different concentrations of inhibitor in 1.0 M HCl solution at 30◦ C
obtained from Tafel polarization curves.
−Ecorr (mV SCE)
Inhibitor concentration (ppm)
HCl (1 M)
100
200
300
400
500
996
992
985
981
980
977
ba (mV dec−1 )
0.43
0.58
0.66
0.76
0.86
0.88
bc (mV dec−1 )
0.49
0.59
0.64
0.72
0.76
0.81
Icorr (mA cm−2 )
2.41
0.91
0.62
0.43
0.22
0.15
θ
—
0.62
0.74
0.82
0.90
0.93
IE (%)
—
62.30
74.30
82.20
90.90
93.80
Table 3: Effect of temperature on the corrosion parameters of zinc in 1.0 M HCl and 1.0 M HCl + 500 ppm of inhibitor.
System
Ecorr (mV SCE)
−996
−1002
−1001
−999
−1001
−977
−979
−983
−985
−987
T (K)
303
313
323
333
343
303
313
323
333
343
1.0 M HCl
1.0 M HCl + 500 ppm inhibitor
0.8
IE (%)
—
—
—
—
—
93.80
91.70
91.80
90.50
89.90
−1.8
0.6
−2
Blank
0.4
−2.2
0.2
−2.4
log K/T
log K
Icorr (Ma cm−2 )
2.41
2.81
3.96
4.73
5.58
0.15
0.231
0.322
0.445
0.561
0
−0.2
−0.4
Inhibitor
−2.6
−2.8
−3
−0.6
−3.2
−0.8
−3.4
2.9
3
3.1
3.2
2.9
3.3
Figure 3: Relation between log K and the reciprocal of the
absolute temperature of zinc electrode in 1.0 M HCl devoid of and
containing 500 ppm of an inhibitor compound.
An alternative formulation of the Arrhenius equation is
the transition state equation [22, 23]
−ΔH ∗
RT
ΔS∗
exp
,
exp
Nh
R
RT
3.1
3.2
3.3
1000/T (K−1 )
1000/T (K−1 )
K=
3
(6)
where h is Planck’s constant, N is Avogadro’s number, ΔS∗
is the entropy of activation, and ΔH ∗ is the enthalpy of
activation.
Figure 4: Arrhenius’ plot of log K/T versus 1/T for the dissolution
of zinc in 1.0 M HCl in the absence and presence of inhibitor.
Figure 4 shows a plot of log(K/T) against (1/T). Straight
lines are obtained with a slope of (−ΔH ∗ /2.303R) and an
intercept of (log R/Nh + S∗ /2.303R) from which the values
of ΔH ∗ and ΔS∗ are calculated and listed in Table 4.
As it can be seen from Table 4, the positive values of
ΔH ∗ reflect a strong chemisorption of the inhibitor on
the surface. The values of entropy of activation ΔS∗ in the
absence and presence of the studied extract compound are
negative. This implies that the activated complex in the rate
ISRN Corrosion
5
Table 4: Activation parameters of the dissolution reaction of zinc in 1.0 M HCl in the absence and presence of 500 ppm of inhibitor.
Ea (kJ mol−1 )
9.832
14.768
System
1.0 M HCl
1.0 M HCl + 500 ppm inhibitor
ΔH ∗ (kJ mol−1 )
16.12
25.12
ΔS∗ (J mol−1 )
−209.355
−216.105
Table 5: Impedance data and surface coverage for zinc electrode in 1.0 M HCl in absence and presence of different concentrations of
inhibitor.
Inhibitor conc. (ppm)
0.00
100
200
300
400
500
Rs (Ω cm2 )
0.95
1.20
1.42
2.02
2.30
2.85
Rct (Ω cm2 )
51
230
345
378
418
470
Cdl (μF cm−2 )
22.30
19.80
17.33
15.47
11.08
9.78
Rct
θ
—
0.78
0.85
0.86
0.87
0.89
250
6
200
Figure 5: Electrical equivalent circuit (Rs Ω: uncompensated solution resistance, Rct : charge transfer resistance, and Cdl : double layer
capacitance).
−Zi (Ω cm 2)
Rs
Cdl
IE (%)
—
77.80
85.20
86.50
87.80
89.20
4
3
150
5
2
100
50
1
0
determining step represents an association rather than a
dissociation step [23].
3.4. Electrochemical Impedance Spectroscopy Studies. Electrochemical impedance spectroscopy (EIS) measurements
were carried over the frequency range from 10 kHz to
100 mHz at open circuit potential. The sample equivalent
Randle circuit for studies is shown in Figure 5 obtained
for zinc in 1.0 M HCl with and without inhibitor, where
Rs (Ω cm2 ) represents the solution and corrosion products
film; the parallel combination of resistor, Rct (charge transfer
resistance), and capacitor Cdl (double layer capacitance)
which represents the corroding interface.
Figure 6 shows the Nyquist plots for zinc in 1.0 M HCl
solution without and with different concentrations of
inhibitor at 30◦ C. The Nyquist plots were regarded as one
part of a semicircle. The charge transfer resistance values
(Rct ) were calculated from the difference in impedance at
lower and higher frequencies, as suggested by Haruyama and
Tsuru [24].
The impedance quantitative results were listed in Table 5.
It is seen that the Rct values of the investigated compounds
increase with increasing inhibitor concentration. At the same
time the Cdl has opposite trend in the whole concentration
range. These observations clearly bring out the fact that the
corrosion of zinc in 1.0 M HCl is controlled by a charge
transfer process. The decrease of Cdl by the increase of
0
100
200
300
400
500
Zr (Ω cm2 )
Figure 6: The Nyquist plots for zinc electrode in 1.0 M HCl in
absence and presence of different concentrations of inhibitor: (1)
0.00 ppm, (2) 100 ppm, (3) 200 ppm, (4) 300 ppm, (5) 400 ppm,
and (6) 500 ppm.
the inhibitor concentration is due to the adsorption of the
inhibitor compound on the electrode surface leading to a
film formation on the Zn surface, and then decreasing the
extent of dissolution reaction [25].
4. Inhibition Mechanism
The inhibitive effect of the investigated water extract as
mentioned above from the experimental results was a
retardation of the dissolution process of zinc metal in HCl
solution. It can be proposed that the effective compounds in
this extract contain functional groups, which can operate as
adsorption centers.
The shape of the molecule and its size and the presence
of conjugate double bonds and other groups (such as OH)
in α-terpineol and the oxygen in 1,8-cineole, which are
electron rich and serve as good adsorption sites onto the
metal surface, are therefore responsible for the inhibitory
action of the investigated extract on zinc in HCl solutions.
6
ISRN Corrosion
The adsorption of an organic adsorbate on the surface
of a metal can be regarded as a substitutional adsorption
process between organic compound in aqueous phase and
water molecules adsorbed onto the electrode surface [26]
Org.(aq) + xH2 O(s) −→ Org.(s) + xH2 O(aq)
(7)
where (x) is the size ratio, which is the number of water
molecules replaced by one molecule of organic adsorbate.
The above process attains equilibrium when
μ org.(aq) + μxH2 O(s) ←→ μ org.(s) + μxH2 O(aq)
(8)
where μ is the chemical potential.
5. Conclusions
(1) There is a good agreement among the results
obtained by different techniques of measurements.
(2) E. cardamomum extract have high inhibitory effect on
the corrosion of zinc in 1.0 M HCl and the inhibition
efficiency increase with increasing its concentration.
(3) The inhibitory effect of E. cardamomum extract
results from its adsorption on the metallic surface
through its electron rich functional groups.
(4) The adsorption of the investigated water extract on a
zinc surface follows Langmuir’s adsorption isotherm.
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Ceramics
Hindawi Publishing Corporation
http://www.hindawi.com
International Journal of
Biomaterials
Nanoscience
Volume 2014
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 2014